PackageKit is a system designed to make installing and updating software on
your computer easier. The primary design goal is to unify all the software
graphical tools used in different distributions, and use some of the latest
technology like PolicyKit to make the process suck less.

The actual nuts-and-bolts distro tool (yum, apt, conary, etc) is used by
PackageKit using compiled and scripted helpers. PackageKit isn't meant to
replace these tools, instead providing a common set of abstractions that can
be used by standard GUI and text mode package managers.

PackageKit itself is a system activated daemon called packagekitd. Being
system activated means that it's only being run when the user is using a text
mode or graphical tool, and quits when it's no longer being used. This means
we don't delay the boot sequence or session startup and don't consume memory
when not being used.

gnome-packagekit is the name of the collection of graphical tools for
PackageKit to be used in the GNOME desktop.